1. Field of the Invention
This invention relates to systems for applying a thin metallic coating to articles being processed in a continuous high throughout manner, and more particularly to vacuum chamber coating systems, workpiece transport, vacuum valving arrangements and multiple sputter source arrays therefor, for continuously handling and uniformly coating across work pieces of large area and width.
2. Description of the Prior Art
Arrangements for continuous coating of work pieces by vacuum processing techniques such as sputtering have evolved from variations on the original bell jar to rather sophisticated in-line systems, with air locks to enable the atmosphere in the coating area of the system to be controlled, and special conveyers cooperating with complex positioning or loading means and valving means.
Many of such continuous processing systems have been devised for smaller work pieces such as substrates or wafers for solid state electronic component fabrication. Recently, advances in the efficiency, uniformity of deposition, and speed of sputtering sources (see for example, pending U.S. application Ser. No. 805,485 filed June 10, 1977 to R. M. Rainey for "Target Profile for Sputtering Apparatus") now issued as U.S. Pat. No. 4,100,055 have made it possible to consider the metalization of workpieces of larger area by the sputtering process, on a production line continuous basis.
However, it has normally been required to impose rotational or other complex motion to the object being coated. This is an elaborate mechanical requirement which is unsuitable in a system to be run on a production line continuous basis. Other systems have attempted to make use of non-circular "line" sources to provide the coating material, but such sources have not provided the requisite degree of uniformity over wide horizontal workpieces, nor have they provided a suitable level of uniformity and coverage for both vertical and horizontal surfaces of wide workpieces. For the same reasons of problems with coverage and uniformity, arrays of circular-cathode sputtering sources for wide workpieces have not been successful. Furthermore, the vacuum isolation valves and transport systems for such prior systems have not proved very suitable for handling large workpieces, because of the special problems unique to the vacuum processing of wide workpieces.
As noted, because the coating process is conducted in a controlled atmosphere, typically one which is evacuated to low pressure, and which can have in addition a rare (inert) gas at low pressure, air locks must be employed, and isolation valves utilized. These in turn must interface with conveyer apparatus transporting work pieces into the system on a continuous basis. The requirements of size of work piece and high throughput impose conflicting requirements which the design of the system must address. Since the workpieces are large in width, the isolation valve must be of large capacity. Yet the valve may not be axially deep (in the direction of the path of the work pieces), since the valve constitutes a discontinuity in the conveying system which must be made small in order not to inhibit the transport of workpieces through the valve, or increase the time needed to evacuate a given airlock.
Moreover, the increased area and capacity of the valve mean that greatly increased strength is needed to maintain the required level of controlled atmosphere. Again, this conflicts with the need to maintain compactness, as well as the need to keep at a minimum the initial mass of the valve, since stress and wear during continuous operation must be minimized for reliability. Another similar, difficult to address need is to keep the space above and across the conveying means immediately ahead of the valve free of any possibility of interference with the opening and closing of the isolation valve. This must be the case in order to permit workpieces to be advanced continuously to points proximate the valve, so that a continuous feed for high throughput is feasible.
Prior isolation valves have fallen short of these requirements, especially in capacity for admitting workpieces of large frontal area, and particularly width. None have had a means for distributing the sealing forces evenly about an elongated or wide gate member without undue interference with the space ahead of the gate, through which workpieces would be approaching in a production system. Thus, designs may be seen with a plurality of air cylinders bearing on various points of the closure member, or having lever arms bearing centrally or toward the sides of the closure member, and positioned, at least in the closed position, in a manner potentially interfering with the progress of work pieces on any adjacent conveying means. Also, prior valves, because of such closure mechanism designs, have not been of an overall thinness to assure that conveyer means on either side of the valve would be separated by a gap small enough not to inhibit the transport of work pieces.
Further, the means by which the closure members of such prior valves have been supported have not been designed to withstand the high inertial loads and consequent wear of rapid cycling, especially with larger valve components of a higher capacity design. Typically such means as pivots, either at one point or acting at two points along an upper edge, have been used to support the closure member. This has made it difficult to completely clear the gate for a more compact design, and to alleviate loading and stress in larger capacity designs.
A successful sputter-coating system with continuous rapid throughput of large workpieces also of course requires that all components be of the greatest possible simplicity, reliability, and responsiveness to command signals. For example, the valve should have a minimum of moving parts, while the conveying means must be capable of working at varying rates, and have the capacity to transfer workpieces within a small area, including the capacity for moving wide workpieces in a compact folded path. Prior systems have not been found to have these attributes.
Finally, the above elements must be combinable into a system which can cause a continuous run of workpieces to smoothly make the transition from the ambient atmosphere to the vacuum processing chamber with its controlled atmosphere, perform the coating over wide workpieces, such as auto grilles or trim panels, with uniformity over both vertical and horizontal surfaces across the piece, and maintain the rate of progress within the coating section of the chamber at a steady non-varying rate for optimum operation of the coating process.